The present invention relates to digital switches and, in particular, to a non-blocking digital switching matrix for both time and space switching in a telephone system which can be expanded without requiring reconfiguration of existing data paths.
In general, computer control of line switching in digital communication systems is well known. Reference in this regard is made to Martin, "Telecommunications and the Computer", Prentice-Hall, 1969, and Joel, "Circuit Switching: Unique Architecture and Applications," Computer, June, 1979, pages 10-22. Digital switching matrices typically include components for time division multiplexing a plurality of channels onto a single line. In time division multiplexing digitized samples from each of the plurality of channels are provided on the common line in sequence. A "frame" of data is thus generated, comprising a plurality of data bytes generated on the commmon line during a plurality of time slots, each time slot associated with a particular channel in accordance with a relative position of the time slot within the frame.
The digital switching matrices typically also include space division stages which, during a given time slot, communicate a sample present on one line to a different line. An example of a 3-stage space division switching system is described in U.S. Pat. No. 3,458,658 to E. Aro, July 29, 1969.
Another component of typical switching systems is the so-called time slot interchange (TSI) circuit. Time slot interchange circuits typically store each of the data bytes (digital samples) in a frame and then output them in a different order, i.e. in a different relative time slot than in which received. TSI circuits also often include space switching capabilities. Such a TSI circuit is described in U.S. Pat. No. 3,715,505 issued Feb. 6, 1973 to Gordon et al.
It is desirable that the digital switching matrix be non-blocking, that is, that an effective connection can be made between any two channels without having to re-route existing connections in the matrix, regardless of effective connections already established. Non-blocking switching systems are discussed in "A Study of Non-Blocking Switching Networks" by Charles Clos, the Bell System Technical Journal, March 1953, pages 406-424. An example of a non-blocking digital switching system is described in U.S. Pat. No. 3,458,659 issued July 29, 1969 to S. Sternung.
It is desirable that a digital switch be capable of expansion while remaining non-blocking and not requiring reconfiguration of the existing system. Further, it is desirable that the digital switching system be of a modular architecture, so that the system may be expanded in stages.